This invention relates to parallel printers and in particular to an improved parallel printer wherein timing pulses generated by a photo detection circuit are utilized to provide a print-off signal to the print command circuit to indicate completion of the print cycle.
Although printers utilizing selectively rotated character rings wherein the print characters disposed thereon are selectively rotated to a print position in response to a print command signal are well known, such printers have been less than completely satisfactory. In order to insure that the print-off signal is not applied until the character ring has been sufficiently rotated toward the rest position so that the next print cycle can be commenced, it is necessary to apply a print-off signal to the print command circuit. Accordingly, photo detection circuits, reed switches, microswitches, etc. have been utilized to provide a print-off signal to the print command circuit. The inclusion of such signal generating mechanisms is both complicated and costly. One attempt to overcome this problem has been the use of mono-stable multivibrators adapted to apply a print-off signal at a certain time interval after the print command signal has begun the print cycle. However, in order to utilize the mono-stable multivibrator effectively, the time interval must be for the worst condition, taking into account such variations as the ambient temperature and mechanical and electrical delays. Thus, such a method reduces the amount of printed lines per unit of time by increasing the time of each print cycle hence decreasing the cost of the printing operation.